Ultrastable laser interferometry for earthquake detection with terrestrial and submarine cables

Detecting ocean-floor seismic activity is crucial for our understanding of the interior structure and dynamic behavior of the Earth. However, 70% of the planet’s surface is covered by water and seismometers coverage is limited to a handful of permanent ocean bottom stations. We show that existing telecommunication optical fiber cables can detect seismic events when combined with state-of-the-art frequency metrology techniques by using the fiber itself as the sensing element. We detected earthquakes over terrestrial and submarine links with length ranging from 75 to 535 km and a geographical distance from the earthquake9s epicenter ranging from 25 to 18,500 km. Implementing a global seismic network for real-time detection of underwater earthquakes requires applying the proposed technique to the existing extensive submarine optical fiber network.